1. Field Of The Invention
The present invention relates to a sealing ring inserted into the radial space between two relatively movable cylindrical surfaces of a first and a second machine part, in which the cylindrical surfaces surround one another coaxially. The invention includes a first element statically fixing and sealing the first machine part, and a second element for dynamically sealing the second machine part. The first element is formed by a retaining ring made of a polymeric material pierced by a relief groove and engaging the first machine part. The first element also includes an annular-shaped lip seal situated in front of the relief groove which is acted upon by the pressure of the medium to be sealed and elastically deforms in response to a pressure differential above a preselected minimum to disengage from the first machine part.
2. Description Of The Prior Art
A sealing ring is shown in German Patent No. 32 44 209. That sealing ring is designed as a doctor seal element and has a sealing body having two doctoring lips spaced axially from one another. The sealing ring has at least one sealing part projecting outwardly from the sealing body transversely to the axis of the sealing ring which abuts sealingly, and under prestressing, against an axially adjoining counter-sealing surface. The sealing ring is designed to be used as a secondary sealing device and is arranged on the side of a primary sealing device facing away from the medium to be sealed. During normal use, the annular space which is between the primary and the secondary sealing devices can gradually fill up with the medium to be sealed, for example oil, leading to a pressure build-up in this space. The objective which underlies the sealing ring of German Patent No. 32 44 209 is to construct the sealing ring in such a way that the sealing device is prevented from being forced out due to high pressure, while forgoing relief boreholes in the hydraulic cylinder. In the event of rising oil pressure, the oil present in the annular space between the primary sealing device and the sealing ring is released, by a relief groove past a lip seal, to the surroundings in order. This oil release indicates that the primary sealing device is defective and therefore should be replaced. Because, under excessive pressure, the oil escapes through the relief groove in the direction of the surroundings, impurities are intended to be prevented from penetrating into the space to be sealed.